Production method of zinc-plated low-alloy high-strength steel with 380MPa-grade yield strength for automobile structure

Abstract

The invention discloses a production method of zinc-plated low-alloy high-strength steel with the yield strength of 380MPa for an automobile structure. The production method comprises a smelting-continuous casting production process; the molten steel for a casting machine comprises the following components in percentage by mass: 0.05 to 0.08 percent of C, less than or equal to 0.06 percent of Si, 0.6 to 0.9 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.010 percent of S, 0.015 to 0.050 percent of Alt, 0.02 to 0.04 percent of Nb, 0.02 to 0.04 percent of Ti, 0.0008 to 0.0020 percent of Ca and less than or equal to 0.0070 percent of N; (2) a hot rolling production process; (3) pickling and cold rolling; and (4) carrying out continuous hot galvanizing and finishing processes. The mechanical properties of the galvanized low-alloy high-strength steel meet the requirements that the yield strength ReL is 380-480 MPa, the tensile strength Rm is 440-560 MPa, and the ductility A80 is larger than or equal to 19%.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical plates, and in particular relates to a production method of galvanized low-alloy high-strength steel for automobile structures with a yield strength of 380 MPa. Background Art

[0002] my country's automobile sales have ranked first in the world and are growing rapidly. With the explosive growth of automobile production, the environmental and energy crises are becoming increasingly severe. Energy conservation and emission reduction have become major issues facing the automobile manufacturing industry. An effective measure to reduce emissions and fuel consumption is to make the car lightweight. However, lightweighting is contradictory to automobile safety. The way to reduce the weight and achieve lightweight while ensuring automobile safety is to use various advanced high-strength steel materials. In order to meet the development needs of weight reduction, energy saving and safety in the modern automobile industry, domestic and foreign steel companies that have the ability to produce high-strength steel are increasing the research and development of hot-dip galvanized high-strength steel plates for automobiles. In automobile manufacturing, the proportion of hot-dip galvanized low-alloy high-strength steel is gradually increasing. Galvanized low-alloy high-strength steel has high strength and yield strength ratio. It is widely used for its excellent mechanical strength, ductility, welding performance and corrosion resistance. It is mainly used in left and right cross beams, longitudinal beams, interior door panels, seats and other structural parts.

[0003] As a higher strength grade product of low alloy high strength steel, galvanized low alloy high strength steel with yield strength of 380MPa for automobile structure has good formability and high strength. It is mainly used for automobile structural parts and reinforcements to meet the needs of different customers. With the development of new energy vehicles, the demand is increasing and it has a broad market application space.

[0004] At present, the yield strength 380MPa grade low alloy steel produced by Panzhihua Iron and Steel Research Institute Co., Ltd. of Panzhihua Iron and Steel Group (a yield strength 380MPa grade low alloy steel and splicing method, application number 202210361876.3) has a high content of Si: 0.15-0.50% and Mn: 0.75-1.30% in the composition design, which affects the product cost and surface quality, which is different from the composition design of the present invention; the yield strength 380MPa grade iron-zinc coated steel plate produced by Wuhan Iron and Steel Co., Ltd. (a yield strength 380MPa grade iron-zinc coated steel plate and production method, application number 201611178665.7) has a composition design of C: 0.09-0.10%, does not contain T i element, which is different from the composition design of the present invention; the 380MPa grade Nb-containing low-alloy high-strength steel produced by Maanshan Iron and Steel Co., Ltd. (a 380-500MPa grade Nb-containing low-alloy high-strength steel and its production method, application number 201910717618.2) has a composition design of Si≤0.5%, does not contain Ti element, and the coiling temperature is 490℃-540℃, which affects the product surface and production rhythm, and is different from the composition and process design of the present invention. Summary of the invention

[0005] The purpose of the present invention is to provide a method for producing galvanized low-alloy high-strength steel with a yield strength of 380MPa for automobile structures. The galvanized low-alloy high-strength steel with a yield strength of 380MPa has high strength and yield strength ratio, and is widely used for its excellent mechanical strength, ductility, welding performance and corrosion resistance, meeting the application requirements of lightweight, high-strength and high-corrosion resistance of automobile body structures. Mechanical properties meet: yield strength R eL : 380-480MPa, tensile strength R m : 440-560MPa, elongation A 80 ≥19%.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for producing galvanized low-alloy high-strength steel with a yield strength of 380 MPa for automobile structure, comprising:

[0008] (1) Smelting-continuous casting production process: molten iron pretreatment-converter-LF refining-slab continuous casting; oxygen blowing and decarburization are carried out in the converter top and bottom combined blowing smelting to raise the temperature; aluminum iron, manganese iron, etc. are added during the converter steelmaking process for deoxidation and alloying, and the P and S components are controlled to prevent the steel liquid from overoxidation. The steelmaking temperature is ≥1600℃; LF refining outside the furnace adopts the LF full-process argon blowing process to adjust the target composition according to the molten steel composition, and the molten steel composition for the casting machine is calculated as C in mass percentage: 0.05-0. 08%, Si≤0.06%, Mn: 0.6-0.9%, P≤0.020%, S≤0.010%, Alt: 0.015-0.050%, Nb: 0.02-0.04%, Ti: 0.02-0.04%, Ca: 0.0008-0.0020%, N≤0.0070%, the rest are Fe and impurities; slab continuous casting superheat 15-40℃, pulling speed controlled at 1.0-1.8m / min;

[0009] (2) Hot rolling production process: heating of ingot - rough rolling - finishing rolling - coiling; ingot furnace time is 170-240 min, furnace temperature is 1200-1280°C, rough rolling is carried out by 3+3 mode 2-stand rolling mill, finishing rolling is carried out by 7-stand rolling mill, finishing rolling start temperature is 940-1040°C, finishing rolling final temperature is 850-900°C, hot rolled steel strip thickness is 2.7-5.1 mm; cooling is carried out by laminar cooling equipment, coiling temperature is 550-600°C;

[0010] (3) Pickling cold rolling process: After the hot-rolled steel strip is pickled to remove the surface iron oxide scale, it is cold-rolled in a 5-stand cold rolling mill with a cold rolling reduction rate of 50-70% and a thickness of 0.8-2.5 mm;

[0011] (4) Continuous hot-dip galvanizing and skin-passing process: The cold-hardened steel strip is unrolled and welded for continuous production. The furnace speed is 55-110 m / min, the average heating temperature is 750-800°C, and it is slowly cooled to 640-680°C, then cooled to 440-480°C, and the temperature of entering the zinc pot is 440-480°C. The skin-passing elongation is 0.5-1.4%, and the tensile elongation is ≤0.3%.

[0012] Furthermore, the galvanized low alloy high strength steel is calculated by mass percentage as C: 0.055-0.078%, Si 0.02-0.05%, Mn: 0.7-0.9%, P 0.013-0.017%, S 0.002-0.006%, Alt: 0.028-0.039%, Nb: 0.028-0.039%, Ti: 0.021-0.028%, Ca: 0.0009-0.0016%, N 0.0031-0.0048%, and the rest is Fe and impurities.

[0013] Furthermore, the hot rolling process: the furnace time is 178-232min, the furnace temperature is 1212-1276℃, the finishing rolling start temperature is 945-1038℃, and the finishing rolling final temperature is 861-898℃.

[0014] Furthermore, the pickling cold rolling process: speed 57-108m / min, soaking temperature 755-798℃, slow cooling temperature 642-675℃, fast cooling temperature 442-479℃, zinc pot entry temperature 440-478℃.

[0015] Furthermore, the tensile elongation is 0.02-0.29%.

[0016] Furthermore, the mechanical properties of the produced galvanized low alloy high strength steel meet the following requirements: yield strength ReL: 414-447 MPa, tensile strength Rm: 488-530 MPa, and elongation A80: 21.5-27.5%.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are:

[0018] The 380MPa yield strength galvanized low alloy high strength steel of the present invention has high strength and yield strength ratio, and is widely used for its excellent mechanical strength, ductility, welding performance and corrosion resistance, meeting the application requirements of lightweight, high strengthening and high corrosion resistance of the automotive industry. Mechanical properties meet: yield strength R eL : 380-480MPa, tensile strength R m : 440-560MPa, elongation A 80 ≥19%. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below in conjunction with the accompanying drawings.

[0020] Figure 1 The microstructure diagram of the embodiment. DETAILED DESCRIPTION

[0021] The present invention is described in detail below through specific examples. The examples are only intended to help understand the present invention but are not intended to limit the present invention.

[0022] Example

[0023] According to the above steelmaking production process requirements, the actual slab chemical composition is shown in Table 1.

[0024] Table 1 Chemical composition of the present invention (wt%)

[0025]

[0026] According to the above hot rolling process requirements, the hot rolling thickness is 2.7-5.1mm, and the actual process is shown in Table 2.

[0027] Table 2 Hot rolling process of the embodiment of the present invention

[0028]

[0029] According to the above cold rolling, hot dip galvanizing and skin-passing process requirements, the cold rolling thickness is 0.8-2.5mm, and the actual hot dip galvanizing and skin-passing process is shown in Table 3.

[0030] Table 3 Hot-dip galvanizing and skin-passing process of the embodiment of the present invention

[0031]

[0032] The mechanical properties of the steel strip according to the embodiment of the present invention were tested, and the test results are shown in Table 4.

[0033] Table 4 Mechanical properties of the steel strip in the embodiment of the present invention

[0034]

[0035] From the data in Table 4, it can be seen that the mechanical properties of the galvanized low-alloy high-strength steel for automobile structure with a yield strength of 380 MPa in the present invention meet the following requirements: yield strength R eL : 414-447MPa, tensile strength R m : 488-530MPa, elongation A 80 : 21.5-27.5%. In summary, the steel strip products obtained by the process have been used by users and have suitable performance and can be promoted for use.

[0036] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for producing galvanized low-alloy high-strength steel for automobile structure with a yield strength of 380 MPa, characterized in that: include: (1) Smelting-continuous casting production process: molten iron pretreatment-converter-LF refining-slab continuous casting; In the converter top and bottom combined blowing smelting, oxygen blowing, decarburization and heating are carried out, and aluminum iron, manganese iron and the like are added in the converter tapping process for deoxidation and alloying, and the P and S components are controlled to prevent the molten steel from being overoxidized, and the tapping temperature is ≥1600℃; LF out-of-furnace refining adopts LF full-process argon blowing process, and the target composition is adjusted according to the molten steel composition, and the molten steel composition for the casting machine is calculated by mass percentage as C: 0.05-0.08%, Si≤0.06%, Mn: 0.6-0.9%, P≤0.020%, S≤0.010%, Alt: 0.015-0.050%, Nb: 0.02-0.04%, Ti: 0.02-0.04%, Ca: 0.0008-0.0020%, N≤0.0070%, and the rest is Fe and impurities; the slab continuous casting superheat is 15-40℃, and the pulling speed is controlled at 1.0-1.8m / min; (2) Hot rolling production process: heating of ingot - rough rolling - finishing rolling - coiling; ingot furnace time is 170-240 min, furnace temperature is 1200-1280°C, rough rolling is carried out by 3+3 mode 2-stand rolling mill, finishing rolling is carried out by 7-stand rolling mill, finishing rolling start temperature is 940-1040°C, finishing rolling final temperature is 850-900°C, hot rolled steel strip thickness is 2.7-5.1 mm; cooling is carried out by laminar cooling equipment, coiling temperature is 550-600°C; (3) Pickling cold rolling process: After the hot-rolled steel strip is pickled to remove the surface iron oxide scale, it is cold-rolled in a 5-stand cold rolling mill with a cold rolling reduction rate of 50-70% and a thickness of 0.8-2.5 mm; (4) Continuous hot-dip galvanizing and skin-passing process: The cold-hardened steel strip is unrolled and welded for continuous production. The furnace speed is 55-110 m / min, the average heating temperature is 750-800°C, and it is slowly cooled to 640-680°C, then cooled to 440-480°C, and the temperature of entering the zinc pot is 440-480°C. The skin-passing elongation is 0.5-1.4%, and the tensile elongation is ≤0.3%.

2. The method for producing galvanized low alloy high strength steel for automobile structure with a yield strength of 380 MPa according to claim 1, characterized in that: The galvanized low alloy high strength steel comprises, by mass percentage, C: 0.055-0.078%, Si 0.02-0.05%, Mn: 0.7-0.9%, P 0.013-0.017%, S 0.002-0.006%, Alt: 0.028-0.039%, Nb: 0.028-0.039%, Ti: 0.021-0.028%, Ca: 0.0009-0.0016%, N 0.0031-0.0048%, and the rest is Fe and impurities.

3. The method for producing galvanized low alloy high strength steel for automobile structure with a yield strength of 380 MPa according to claim 1, characterized in that: Hot rolling process: furnace time 178-232min, furnace temperature 1212-1276℃, finishing rolling start temperature 945-1038℃, finishing rolling final temperature 861-898℃.

4. The method for producing galvanized low alloy high strength steel for automobile structure with a yield strength of 380 MPa according to claim 1, characterized in that: Pickling cold rolling process: speed 57-108m / min, soaking temperature 755-798℃, slow cooling temperature 642-675℃, fast cooling temperature 442-479℃, zinc pot entry temperature 440-478℃.

5. The method for producing galvanized low alloy high strength steel for automobile structure with a yield strength of 380 MPa according to claim 1, characterized in that: The tensile elongation is 0.02-0.29%.

6. The method for producing galvanized low alloy high strength steel for automobile structure with a yield strength of 380 MPa according to claim 1, characterized in that: The mechanical properties of the produced galvanized low alloy high strength steel meet the following requirements: yield strength ReL: 414-447MPa, tensile strength Rm: 488-530MPa, elongation A80: 21.5-27.5%.

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